Drought

Issued 2 November 2018

Wetter than average October on the east coast, but rainfall deficiencies persist

Overall, October was somewhat wetter than average for Australia as a whole. October rainfall was above average along the east coast of Australia from the Illawarra in New South Wales, through eastern Queensland, and across large parts of Cape York Peninsula and the Gulf Country. For much of coastal southeast Queensland, and the Northern Rivers and Mid North Coast districts of New South Wales, rainfall was in the highest 10% of historical rainfall totals for the month. However, October rainfall has had little impact on the extent of the area affected by deficiencies since the start of the year.

Meteorological drought is rarely broken in a single event or month; typically regular rainfall over a period of several months is required to remove rainfall deficiencies of the magnitude of those currently in place. A Special Climate Statement will be released shortly discussing the rainfall situation over recent months.

Rainfall was below to very much below average for southeast South Australia, most of Victoria away from the northwest, and all of Tasmania. For Tasmania as a whole it was the third-driest October on record. Rainfall was in the lowest 10% of historical rainfall totals for the month in western to central Tasmania, South and West Gippsland, and other isolated pockets in northern and eastern Australia, including areas scattered along the Victorian coastline. As a consequence, deficiencies have increased in Victoria and agricultural districts of South Australia.

The year to date has been exceptionally dry over the mainland southeast, with significant rainfall deficiencies continuing to affect large areas of eastern Australia at timescales out to around two years duration. Compared to other January to October periods since 1900, year-to-date rainfall has been the third-lowest on record for the Murray–Darling Basin, fourth-lowest for New South Wales, and eighth-lowest for Victoria.

As well as being a very dry year, 2018 has so far been very warm too. High daytime temperatures add to the impact of reduced rainfall; for instance through reduced soil moisture. Australian maximum temperatures for 2018 to date have been the second warmest on record with an anomaly of +1.41 °C (behind 2013 with an anomaly of +1.59 °C). New South Wales (+2.20 °C) has experienced its warmest January–October period on record, while Victoria (+1.48 °C) has tied for equal-warmest (with 2014).

7-month rainfall deficiencies

The southern rainfall season spans April to November and corresponds to the southern agricultural cropping season. For 2018, the southern rainfall season to date has so far seen 7 consecutive months of below average rainfall across much of Australia. Serious or severe rainfall deficiencies persist across much of the eastern mainland, despite above to very much above average rainfall along much of the east coast.

Above average rainfall for October has reduced or removed deficiencies in much of eastern Queensland and adjacent northeastern New South Wales, and also in large parts of Central Australia and inland southern Western Australia.

Conversely, a drier than average month has seen deficiencies increase in both severity and spatial extent in Victoria and in agricultural districts of South Australia.

Large areas of serious of severe rainfall deficiencies are in place in northern, eastern and central southern Victoria; most of New South Wales away from the northeast to central coast and a pocket of the central inland north; large areas of central, western and southern Queensland; eastern South Australia away from the far southeast; and the southeast of the Northern Territory. Deficiencies also affect areas in Western Australia's Southeast Coastal District and the northeast of the Interior District.

10-month rainfall deficiencies

For the year to date, deficiencies have decreased slightly in severity across the northern half of coastal New South Wales and in southeastern Queensland following above-average October rainfall. Rainfall deficiencies nevertheless persist across much of the southeastern quarter of the mainland, and have expanded in central southern and eastern Victoria, and in agricultural districts of South Australia.

Serious or severe rainfall deficiencies affect the eastern half of South Australia except the far southeast; most of Victoria except the southwest; most of New South Wales except the central to northern coastal regions; southwestern Queensland and the Warrego District, pockets along the southern border of Queensland inland of the ranges, and in the Central Highlands and Coalfields District of Queensland; and in Western Australia's South Coastal District.

19-month rainfall deficiencies

The effect of October rainfall on deficiencies at this timescale has been very small—only reducing deficiencies slightly in southeast Queensland and the central coast of New South Wales due to the very large total accumulated rainfall deficits over the longer period.

Rainfall deficiencies have increased across parts of southwestern and southeastern New South Wales, eastern and central southern Victoria, and agricultural districts of South Australia.

Serious or severe rainfall deficiencies are in place across most of New South Wales except the northeast to central coast, and pockets of the southern border country; across eastern to central southern Victoria; much of eastern South Australia away from the southeast and far north; southwestern to central Queensland, and a pocket of the southeastern region inland of the ranges.

Deficiencies also persist in areas along the west coast of Western Australia and in the South West and South Coastal districts of that State.

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Soil moisture

Above average October rainfall across much of the east coast and large parts of Western Australia has resulted in an increase in lower-layer soil moisture (from 10 cm to 100 cm deep) over much of Australia. However, soil moisture has decreased in much of Tasmania, Victoria, and southeastern South Australia where rainfall was below average for the month.

Soil moisture for October was below average for most of the Victoria, the eastern half of South Australia, and southern New South Wales, with much of northern New South Wales and central to southwestern Queensland also affected. Below average soil moisture was also observed across most of Tasmania and scattered areas along the coast of Cape York Peninsula, the Northern Territory, and the Kimberley, Pilbara and far southwest in Western Australia.

Conversely, soil moisture was above average for much of inland southern Western Australia and parts of the southern coastal districts, along the southwestern border regions of the Northern Territory and around the Gulf coast in the Northern Territory and Queensland, the southern Cape York Peninsula, and along the coast in southeastern Queensland and northern to central coast of New South Wales.

October rainfall below average for southeast Australia, but above average on the east coast and in southern Western Australia

Third-driest October on record for Tasmania

Rainfall deficiencies persist across eastern Australia, parts of Central Australia, and some areas of Western Australia

Deficiencies decreased across Central Australia, eastern Queensland, northeastern New South Wales and southern Western Australia; most notable at the 7-month timescale

Lower-level soil moisture below average for October across much of eastern Australia and scattered areas of the coastal north and far southwest Western Australia

Soil moisture details are reported when there are periods of significant rainfall deficits.

Soil moisture data is from the Bureau's Australian Water Resources Assessment Landscape (AWRA-L) model, developed through the Water Information Research and Development Alliance between the Bureau and CSIRO.
See: Australian Landscape Water Balance.

What is drought?

Drought is a prolonged, abnormally dry period when the amount of available water is insufficient to meet our normal use. Drought is not simply low rainfall; if it was, much of inland Australia would be in almost perpetual drought. Because people use water in so many different ways, there is no universal definition of drought. Meteorologists monitor the extent and severity of drought in terms of rainfall deficiencies. Agriculturalists rate the impact on primary industries, hydrologists compare ground water levels, and sociologists define it by social expectations and perceptions.

It is generally difficult to compare one drought to another, since each drought differs in the seasonality, location, spatial extent and duration of the associated rainfall deficiencies. Additionally, each drought is accompanied by varying temperatures and soil moisture deficits.

Rainfall averages, variability and trends

An area experiences a rainfall deficit when the total rain received is less than the average rainfall for that period.

Definitions

Lowest on record - lowest since at least 1900 when the data analysed begin.Severe deficiency - rainfalls in the lowest 5% of historical totals.Serious deficiency - rainfalls in the lowest 10% of historical totals,
but not in the lowest 5%.

Very much below average - rainfalls in the lowest 10% of historical totals.Below average - rainfalls in the lowest 30% of historical totals,
but not in the lowest 10%.Average - rainfalls in the middle 40% of historical totals.Above average - rainfalls in the highest 30% of historical totals,
but not in the highest 10%.Very much above average - rainfalls in the highest 10% of historical totals.

Australian Government drought assistance

Department of Agriculture and Water Resources information and contacts:

Archive

For the week to 13 November 2018, rainfall was recorded in all States and Territories.

At the start of the week, a cloudband developed and extended from Central Australia to the Tasman Sea associated with broad areas of low pressure stretching from the northwest down to the southeast of the continent. Extensive thunderstorm and shower activity resulted in moderate falls across Central Australia, southwest Queensland, and northeastern South Australia. Warm and moist tropical air was dragged into the southeast, ahead of a strong cold front, with embedded thunderstorms generating moderate falls in southern central and northeastern Victoria, parts of southern New South Wales, and western Tasmania. As the cold front and trough moved eastwards, further moderate falls were recorded in southern Queensland, and in northern and eastern New South Wales.

In the second half of the week, a broad surface trough reached from inland Western Australia to the Top End of the Northern Territory and across into the northern tropics of Queensland. Showers and thunderstorms developed along and near the deepening surface trough inland from the west coast , bringing moderate to locally heavy falls to central, eastern parts of the South West Land Division, and the southeast coast of Western Australia. Thunderstorms and moderate falls were also recorded about the northwest Top End of the Northern Territory. In the east, an onshore southeasterly flow produced showers and moderate to locally heavy falls about the north tropical Queensland coast, while an inland surface trough and associated thunderstorms over the Gulf Country and northern interior of Queensland produced moderate falls in the area.

At the end of the week, the surface trough and associated cloudband moved eastwards to the southeast of Western Australia , with further thunderstorm and shower activity generating moderate falls in the Goldfields District and about the State's southeast coast.

Rainfall totals exceeding 50 mm were observed in the northwest Top End of the Northern Territory, the north tropical coast of Queensland, small areas of southeastern New South Wales, and southeast Gascoyne, Goldfields and Southern Interior of Western Australia. Isolated falls exceeding 100 mm were recorded in areas of the Goldfields District in Western Australia; also a small area in the north tropical Queensland coast, including the highest weekly total of 157 mm at Mutarnee Store.

Rainfall totals between 25 mm and 50 mm were recorded across large parts of central and small areas of southeast Western Australia; in the northwest Top End and southern parts of the Northern Territory; areas of northern and southwest Queensland; northwest, southeast and east coast New South Wales; northeastern and southern central Victoria, and western Tasmania.

Rainfall totals between 10 mm and 25 mm were recorded across much of the central, southeast coast and west Kimberley in Western Australia; in the northwest and southern parts of the Northern Territory; parts of the tropical north, central and southern Queensland; most of New South Wales away from the southwest; small areas in the north and southeast of South Australia; southern and eastern Victoria, and the western half of Tasmania.

Little or no rainfall was recorded in remaining parts of the continent.

Impact of recent rainfall on deficits

The Drought Statement, issued on the 2 November 2018, discussed rainfall deficits over Australia for the 7-month (April–October 2018), the 10-month (January–October 2018) and 19-month (April 2017–October 2018) periods. Rainfall deficit maps are available for these periods as well as for standard periods.

The maps below show the percentage of mean rainfall that has been received for the rainfall deficit period for the 7-month, 10-month and 19-month periods ending 13 November 2018.

Rainfall for the period 1 April 2018 to 13 November 2018

Large areas of serious or severe rainfall deficiencies affect areas in Western Australia's Southeast Coastal District and the northeast of the Interior District; eastern South Australia away from the far southeast; and the southeast of the Northern Territory. Deficiencies are also in place in northern, eastern and central southern Victoria; most of New South Wales away from the northeast to central coast and a pocket of the central inland north; and large areas of central, western and southern Queensland.

Rainfall in the past week has eased deficiencies somewhat in Central Australia, northeastern South Australia, parts of northwestern and central New South Wales, and southwest Queensland.

Affected areas of southern coastal Western Australia, southeastern South Australia, eastern and northern Victoria generally received between 50% and 80% of average rainfall for the period. Affected areas in central and southern New South Wales, and the north tropical Queensland coast have received between 30% and 60% of average, while remaining affected areas have received less than 30% of average.

Rainfall for the period 1 January 2018 to 13 November 2018

Large areas of serious or severe rainfall deficiencies affect areas in Western Australia's Southeast Coastal District and the northeast of the Interior District; eastern South Australia away from the far southeast; and the southeast of the Northern Territory. Deficiencies are also in place in northern, eastern and central southern Victoria; most of New South Wales away from the northeast to central coast and a pocket of the central inland north; and large areas of central, western and southern Queensland.

Rainfall in the past week has eased deficiencies somewhat in Central Australia, northeastern South Australia, northwestern and central New South Wales, and southwest Queensland.

Affected areas of southern coastal Western Australia, southeastern South Australia, eastern and northern Victoria generally received between 50% and 80% of average rainfall for the period. Affected areas in central and southern New South Wales, and the north tropical Queensland coast have received between 30% and 60% of average, while remaining affected areas have received less than 30% of average.

Rainfall for the period 1 April 2017 to 13 November 2018

Serious or severe rainfall deficiencies persist at the 19-month time period in areas along the west coast of Western Australia and in the South West and South Coastal districts of that State. Deficiencies are also in place across much of eastern South Australia away from the southeast and far north; eastern to central southern Victoria; across most of New South Wales except the northeast to central coast, and pockets of the southern border country; and in southwestern to central Queensland, and a pocket of the southeastern region inland of the ranges.

During the last week, rain that fell has eased deficiencies very slightly in a small area of northwest New South Wales, but had little impact elsewhere at this timescale.

Rainfall in affected areas of Western Australia, southeast South Australia and Victoria have generally received between 80% and 60% of average for the period. Remaining areas of New South Wales, northeastern South Australia, and southwestern Queensland have received between 60% and 30% of average rainfall for the period.